Catalyst system for olefin oligomerization and method for preparing olefin oligomer by using same

ABSTRACT

Disclosed are a catalyst system capable of selectively oligomerizing olefins including ethylene and a method for preparing an olefin oligomer by using the same and, specifically, a novel catalyst system capable of trimerizing and tetramerizing olefins, unlike olefin oligomerization catalyst systems that have been reported so far, and a method for preparing an olefin oligomer by using the same. The present invention provides a catalyst system for olefin oligomerization, the catalyst system comprising: a ligand compound represented by chemical formula 1 or 2; a chromium compound; a metal alkyl compound; and an aliphatic or alicyclic hydrocarbon solvent.

TECHNICAL FIELD

The present invention relates to a catalyst system for olefinoligomerization and a method for preparing an olefin oligomer by usingthe same, and more particularly, a novel catalyst system capable oftrimerizing and tetramerizing olefins, and a method for preparing anolefin oligomer by using the same.

BACKGROUND ART

A linear alpha-olefin is widely used commercially as an importantmaterial used in comonomers, cleaning agents, lubricants, plasticizers,and the like, and in particular, 1-hexene and 1-octene are frequentlyused as comonomers for controlling the density of polyethylene inpreparation of linear low density polyethylene (LLDPE), etc.

Specifically, in the previously known process of preparing LLDPE, abranch is formed in the polymer backbone with ethylene to becopolymerized with a comonomer such as an alpha-olefin, for example,1-hexene or 1-octene, in order to control the density. Therefore, whenLLDPE having a high comonomer content is produced, the price of thecomonomer may occupy a great part of the production cost. Therefore,various attempts have been made to reduce the production cost of thecomonomer. In addition, since the alpha-olefin has different applicationfields or market size according to kinds thereof, technologies forselectively producing specific alpha-olefins are very commerciallyimportant, and recently, research has been conducted on chromiumcatalyst technologies for producing 1-hexene, 1-octene, and the like,with high selectivity through selective ethylene oligomerization.

For example, as a catalyst system for preparing 1-hexene, etc. bypolymerizing olefins such as ethylene, and the like, a high activity,high-selectivity ethylene trimerization catalyst system using a chromiumtrivalent compound, a pyrrole compound, a non-hydrolyzed aluminum alkyl,and an unsaturated hydrocarbon was published from Philips Co. in 1994(see U.S. Pat. No. 5,376,612), and then 1-hexene was commerciallyproduced from the above catalyst system from 2003. Among variouschromium trivalent compounds, a catalyst system usingtris(2-ethylhexanoate) chromium(III) (Cr(EH)₃, EH=O₂C₈H₁₅) showedparticularly excellent catalytic activity, and a catalyst system usingCr(EH)₃ was intensively studied and commercialized.

The catalyst system using Cr(EH)₃ may be prepared in an unsaturatedhydrocarbon solvent, for example, by adding a mixed solution of triethylaluminum and ethyl aluminum dichloride to an unsaturated hydrocarbonsolvent (such as toluene) in which Cr(EH)₃ and 2,5-dimethylpyrrole aremixed. Typically, since the trimerization reaction of olefin is carriedout in a saturated hydrocarbon solvent such as cyclohexane, theunsaturated hydrocarbon solvent of the prepared catalyst system shouldbe removed by vacuum decompression and then dissolved in the saturatedhydrocarbon solvent such as cyclohexane and then used, or the preparedunsaturated hydrocarbon solution phase catalyst system should be usedfor the trimerization reaction and the unsaturated hydrocarbon solventused for the catalyst preparation should be separated and removed afterthe reaction is completed. In addition, when preparing a catalyst usingCr(EH)₃, a black precipitate is formed as a by-product while a catalystactivating species is formed, and thus a process of filtering the blackprecipitate is required (see U.S. Pat. No. 5,563,312). A process ofremoving an unsaturated hydrocarbon solvent such as toluene, a processof filtering, etc. may be a burden in commercialization. In order toomit the process of removing an unsaturated hydrocarbon solvent, whenthe catalyst system is prepared in an aliphatic hydrocarbon solvent suchas cyclohexane which is subjected to a trimerization reaction, thermalstability of the prepared catalyst is lowered, and thus, the catalyst isinactivated during the trimerization reaction or catalyst selectivity islowered to form a large amount of side reactants in addition to olefintrimer (see U.S. Pat. No. 5,563,312), and an unsaturated hydrocarbon isincluded as an essential component in the catalyst system from PhilipsCo., Ltd.

Therefore, International Patent Publication No. WO2015/133805 disclosesa catalyst system having excellent catalytic activity during olefinpolymerization (trimerization) and a raw material compound of thecatalyst system capable of preparing the catalyst system in a saturatedhydrocarbon solvent without a need of a filtration process due to theabsence of byproduct generated during catalyst preparation. However,there is a problem that, in all of the prior patents, only thetrimerization is selectively conducted in the process of performing theolefin oligomerization.

DISCLOSURE OF THE INVENTION Technical Problem

The present invention provides a catalyst system capable of selectivelyoligomerizing olefins including ethylene and a method for preparing anolefin oligomer by using the same, and specifically, a novel catalystsystem capable of trimerizing and tetramerizing olefins, unlike olefinoligomerization catalyst systems that have been reported so far, and amethod for preparing an olefin oligomer by using the same.

Technical Solution

To solve the above problem, the present invention provides a catalystsystem for olefin oligomerization, the catalyst system including: aligand compound represented by Chemical Formula 1 or 2 below; a chromiumcompound; a metal alkyl compound; and an aliphatic or alicyclichydrocarbon solvent.

In Chemical Formula 1 and 2, E₁ is boron (B), carbon (C), nitrogen (N),silicon (Si), or phosphorus (P), and E₂ is boron (B), carbon (C),nitrogen (N), oxygen (O), silicon (Si), phosphorus (P), or sulfur (S),except that both E₁ and E₂ are carbon (C), B₁ is aluminum (Al), boron(B), nitrogen (N), or phosphorus (P), R₁ to R₆ are each independentlyhydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl grouphaving 3 to 20 carbon atoms, an alkylsilyl group having 1 to carbonatoms, a haloalkyl group having 1 to 20 carbon atoms, an aryl grouphaving 6 to 40 carbon atoms, an arylalkyl group having 7 to 20 carbonatoms, an arylsilyl group having 6 to 20 carbon atoms, an alkylarylgroup having 7 to 20 carbon atoms, an aryloxy group having 6 to 20carbon atoms, a halogen group, or an amino group.

In addition, in Chemical Formula 1 and 2 above, there is provided acatalyst system characterized in that E₁ may be nitrogen (N) and E₂ maybe oxygen (O).

Furthermore, there is provided a catalyst system characterized in thatthe chromium compound may be a compound containing chromium(III) orchromium(II).

In addition, there is provided a catalyst system characterized in thatthe metal alkyl compound may be at least one selected from the groupconsisting of an alkylaluminum compound, an alkylboron compound, analkylmagnesium compound, an alkylzinc compound, and an alkyllithiumcompound.

Further, there is provided a catalyst system characterized in that themolar ratio of the ligand compound, the chromium compound, and the metalalkyl compound may be 0.5:1:1 to 10:1:10,000 with respect to thechromium compound.

Moreover, there is provided a catalyst system characterized in that thealiphatic or alicyclic hydrocarbon solvent may be an aliphatic oralicyclic hydrocarbon solvent having 5 to 13 carbon atoms.

In addition, there is provided a catalyst system characterized in thatthe alicyclic hydrocarbon solvent may be a cycloalkene having 5 to 13carbon atoms.

Furthermore, there is provided a catalyst system characterized in thatthe aliphatic or alicyclic hydrocarbon solvent may be n-heptane,2-methyl hexane, 3-methyl hexane, 3-ethyl pentane, 2,3-dimethyl pentane,2,4-dimethyl pentane, 2,2-dimethyl pentane, 3,3-dimethyl pentane,2,2,3-trimethyl butane, cyclopropene, cyclobutene, cyclopentene,cyclopentane, cyclohexene, cycloheptane, cycloheptene, cyclooctane,cyclooctene, cyclononene, cyclodecane, cyclodecene, or a mixturethereof.

In addition, there is provided a catalyst system characterized in thatthe olefin oligomerization may include a trimerization and atetramerization.

According to another aspect of the present invention, there is provideda method for preparing an olefin oligomer, the method includingoligomerizing olefins in an inert solvent that does not react with acatalyst system in the presence of the catalyst system for olefinoligomerization including: a ligand compound represented by ChemicalFormula 1 or 2 below; a chromium compound; a metal alkyl compound; andan aliphatic or alicyclic hydrocarbon solvent.

In Chemical Formula 1 and 2, E₁ is boron (B), carbon (C), nitrogen (N),silicon (Si), or phosphorus (P), and E₂ is boron (B), carbon (C),nitrogen (N), oxygen (O), silicon (Si), phosphorus (P), or sulfur (S),except that both E₁ and E₂ are carbon (C), B₁ is aluminum (Al), boron(B), nitrogen (N), or phosphorus (P), R₁ to R₆ are each independentlyhydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl grouphaving 3 to 20 carbon atoms, an alkylsilyl group having 1 to carbonatoms, a haloalkyl group having 1 to 20 carbon atoms, an aryl grouphaving 6 to 40 carbon atoms, an arylalkyl group having 7 to 20 carbonatoms, an arylsilyl group having 6 to 20 carbon atoms, an alkylarylgroup having 7 to 20 carbon atoms, an aryloxy group having 6 to 20carbon atoms, a halogen group, or an amino group.

Moreover, there is provided a method characterized in that the inertsolvent may be an aliphatic or alicyclic hydrocarbon solvent having 3 to13 carbon atoms.

Furthermore, there is provided a method characterized in that thealiphatic or alicyclic hydrocarbon solvent may be n-heptane, isobutane,2-methyl hexane, 3-methyl hexane, 3-ethyl pentane, 2,3-dimethyl pentane,2,4-dimethyl pentane, 2,2-dimethyl pentane, 3,3-dimethyl pentane,2,2,3-trimethyl butane, cyclopropane, cyclopropene, cyclobutane,cyclobutene, cyclopentane, cyclopentene, cyclohexane, cyclohexene,cycloheptane, cycloheptene, cyclooctane, cyclooctene, cyclononane,cyclononene, cyclodecane, cyclodecene, or a mixture thereof.

Advantageous Effects

The present invention can provide a novel catalyst system capable ofselectively trimerizing and tetramerizing olefins including ethylene byapplying a compound which is not conventionally employed as a ligandcompound in a catalyst system for oligomerization of olefins, and canprovide a method for preparing 1-hexene and 1-octene with excellentactivity and selectivity using the same.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail. In describing the present invention, if a detaileddescription relating to well-known technology is considered to obscurethe subject matter of the present invention, the detailed descriptionmay be omitted. Throughout the specification, a part is referred to“include” an element, the part does not exclude other elements but mayfurther include other elements unless otherwise indicated.

The present invention discloses a catalyst system for olefinoligomerization, the catalyst system including: a ligand compound; achromium compound; a metal alkyl compound; and an aliphatic or alicyclichydrocarbon solvent.

The catalyst system for olefin oligomerization according to the presentinvention is used in an olefin oligomerization method including a stepfor multimerizing olefins in the presence of the catalyst system.According to the present invention, olefins including ethylene may beselectively trimerized and tetramerized.

Hereinafter, a catalyst system for olefin oligomerization according to aspecific embodiment of the present invention will be described in moredetail.

In the present invention, the ligand compound is a compound representedby Chemical Formula 1 below:

In Chemical Formula 1 and 2, E₁ may be boron (B), carbon (C), nitrogen(N), silicon (Si) or phosphorus (P), and E₂ may be boron (B), carbon(C), nitrogen (N), oxygen (O), silicon (Si), phosphorus (P) or sulfur(S), except that both E₁ and E₂ are carbon (C), and preferably E₁ may benitrogen (N) and E₂ may be oxygen (O).

In addition, B₁ may be aluminum (Al), boron (B), nitrogen (N), orphosphorus (P), and preferably aluminum (Al).

R₁ to R₆ may be each independently hydrogen, an alkyl group having 1 to20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, analkylsilyl group having 1 to 20 carbon atoms, a haloalkyl group having 1to 20 carbon atoms, an aryl group having 6 to 40 carbon atoms, anarylalkyl group having to 20 carbon atoms, an arylsilyl group having 6to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, anaryloxy group having 6 to 20 carbon atoms, a halogen group, or an aminogroup. Here, the aryl group may be an aromatic hydrocarbon functionalgroup such as phenyl, biphenyl, triphenyl, triphenylene, naphthalenyl,anthracenyl, phenalenyl, phenanthrenyl, fluorenyl, pyrenyl, chrysenyl,perylenyl, and azulenyl, an aromatic heterocyclic functional group suchas dibenzothiophenyl, dibenzofuranyl, dibenzoselenophenyl, furanyl,thiophenyl, benzofuranyl, benzothiophenyl, benzoselenophenyl,carbazonyl, indolocarbazolyl, pyridylindolinine, pyrolodipyridinyl,pyrazolyl, imidazolyl, triazolyl, oxazolyl, triazolyl, oxadiazolinyl,oxatriazolyl, dioxazolyl, thiadiazolyl, pyridyl, pyridazinyl, pyrimidyl,pyrazinyl, triazinyl, oxazinyl, oxathiazinyl, oxadiazinyl, indolinine,benzimidazolyl, indazolyl, indoxazinyl, benzoxazolyl, benzisoxazolyl,benzothiazolyl, quinolinyl, isoquinolinyl, cinnolinyl, quinazolyl,quinoxalinyl, naphthyridine, phthalazinyl, pteridinyl, xanthenyl,acridyl, fenazinyl, phenothiazine, phenoxazinyl, benzofuropyridyl,furodipyridyl, benzothienopyridyl, thienopyridyl benzoselenopyridyl, andselenophenodipyridyl, etc.

It is more preferable in terms of stabilization of the central metalthat R₁ to R₆ of Chemical Formula 1 above are each independentlyhydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkylgroup, or an aryl group.

As used herein, the term “olefin oligomerization” means that olefin isoligomerized. Depending on the number of olefins to be polymerized, itis called trimerization or tetramerization, and is collectively calledmultimerization. In particular, the term herein means that 1-hexene and1-octene are selectively prepared from ethylene.

Also, the term “catalyst system” may refer to any composition, compound,or complex, which exhibits catalytic activity with respect to the“olefin oligomerization” by including the following materials or areaction product thereof as a catalyst active species, regardless ofwhether the ligand compound, the chromium compound, the metal alkylcompound, and the aliphatic or alicyclic hydrocarbon solvent are simplymixed, or react with each other to form a separate catalyst activespecies.

In addition, the selective olefin oligomerization reaction is closelyrelated to the catalyst system used. The catalyst system used during theolefin oligomerization reaction includes a chromium compound serving asa main catalyst and a metal alkyl compound serving as a cocatalyst,wherein the structure of the active catalyst may be changed according tothe chemical structure of the ligand, and thus the olefin selectivityand the activity are different.

The present inventors confirmed through experiments that theoligomerization, in particular, the trimerization and thetetramerization of olefin can be performed with high catalytic activityand selectivity, since the electronic and steric environment around thetransition metal can be easily controlled by appropriately controllingthe ligand compound with the catalyst system for olefin oligomerization,the catalyst system including the ligand compound having the specificstructure, the chromium compound, the metal alkyl compound as thecocatalyst, and the aliphatic or alicyclic hydrocarbon as the solvent,and completed the present invention.

In particular, the ligand compound is a hexagonal ring compound in whichat least one hetero element such as boron (B), nitrogen (N), oxygen (O),silicon (Si), phosphorus (P), and sulfur (S) is included in the insideof the hexagonal ring or in a functional group connected to thehexagonal ring, and due to such structural characteristics, the ligandcompound may be applied to the oligomerization catalyst system of olefinto exhibit high oligomerization reaction activity, and in particular,exhibit high selectivity to 1-hexene and 1-octene. This is assumed to bedue to an interaction between adjacent chromium active points.

In the present invention, the chromium compound serves as a maincatalyst, and using the chromium(III)- or chromium(II)-containingcompound is preferred to be able to increase the reaction activity.

The chromium(III) compound may be, for example, chromium carboxylate,chromium naphthenate, chromium halide, chromium dionate, and morespecific examples may include chromium(III)2,2,6,6-tetramethylheptanedionate, chromium(III) 2-ethylhexanoate,chromium(III) tris (2-ethylhexanoate), chromium(III) naphthenate[Cr(NP)3], bis(2-ethylhexanoate) chromium(III) hydroxide,bis(2-butanoate) chromium(III) hydroxide, chromium(III) chloride,chromic bromide, chromic fluoride, chromium(III) acetylacetonate,chromium(III) acetate, chromium(III) butyrate, chromium(III)neopentanoate, chromium(III) laurate, chromium(III) stearate,chromium(III) oxalate, bis(2-ethylhexanoate) chromium(III) hydroxide,etc.

In addition, specific examples of a chromium(II) compound may includechromous bromide, chromous fluoride, chromous chloride, chromium(II)bis(2-ethylhexanoate), chromium(II) acetate, chromium(II) butyrate,chromium(II) neopentanoate, chromium(II) laurate, chromium(II) stearate,chromium(II) oxalate, etc.

Meanwhile, the chromium compounds may be in a dissolved state in analiphatic or alicyclic hydrocarbon solvent. The aliphatic or alicyclichydrocarbon solvent may be, but is not limited to, n-heptane, 2-methylhexane, 3-methyl hexane, 3-ethyl pentane, 2,3-dimethyl pentane,2,4-dimethyl pentane, 2,2-dimethyl pentane, 3,3-dimethyl pentane,2,2,3-trimethyl butane, cyclohexene, cycloheptane, cycloheptene,cyclooctane, cyclooctene, cyclodecane, cyclodecene, or a mixturethereof.

In the catalyst system for olefin oligomerization of an embodiment,chromium(III) 2-ethylhexanoate, chromium(III) acetylacetonate orbis(2-ethylhexanoate) chromium(III) hydroxide is used as a chromiumcompound and it is preferable to dissolve and use this in anhydrouscyclohexene solvent in terms of improving the catalytic activity due tothe difference in solubility of the solvent.

In the present invention, the metal alkyl compound is a cocatalyst ofthe catalyst system for olefin oligomerization, and is not particularlylimited as long as it can be generally used when multimerizing olefinsin the presence of the transition metal catalyst. For example, analkylaluminum compound, an alkylboron compound, an alkylmagnesiumcompound, an alkylzinc compound, an alkyllithium compound, etc. may beused as the metal alkyl compound.

However, in order to exhibit high selectivity and activity in the olefinoligomerization reaction, an alkylaluminum compound may be used as thecocatalyst compound. Specific examples of the alkylaluminum compound mayinclude triethylaluminum, tripropylaluminum, tributylaluminum anddiethylaluminum chloride, diethylaluminum bromide, diethylaluminumethoxide, diethylaluminum phenoxide, ethylaluminum dichloride,ethylaluminum sesquichloride, etc., preferably a mixture oftriethylaluminum, ethylaluminum dichloride, and ethylaluminumsesquichloride can be used, and this case is preferred because not onlycan the water be effectively removed, but also the catalytic activity isimproved by including the electron donor atom.

In the catalyst system for olefin oligomerization according to thepresent invention, the molar ratio of the ligand compound:chromiumcompound:metal alkyl compound may be 0.5:1:1 to 10:1:10,000, andpreferably 0.5:1:100 to 5:1:3,000 in order to increase the selectivityto the linear alpha-olefin and increase the multimerization reactionactivity. However, the present invention is not limited thereto.

In the present invention, the aliphatic or alicyclic hydrocarbon solventmay be preferably a hydrocarbon solvent having 5 to 20 carbon atoms, andmore preferably a hydrocarbon solvent having 5 to 13 carbon atoms.

In addition, in the present invention, the alicyclic hydrocarbon solventmay be a cycloalkene having 5 to 13 carbon atoms including at least onecarbon-carbon double bond in a ring, and preferably a cycloalkene having5 to 13 carbon atoms which satisfies C_(n)H_(2n−2).

Specific examples of such aliphatic or alicyclic hydrocarbon solventsinclude n-heptane, 2-methylhexane, 3-methylhexane, 3-ethylpentane,2,3-dimethylpentane, 2,4-dimethylpentane, 2,2-dimethylpentane,3,3-dimethylpentane, 2,2,3-trimethylbutane, cyclopropene, cyclobutene,cyclopentene, cyclopentane, cyclohexene, cycloheptane, cycloheptene,cyclooctane, cyclooctene, cyclononene, cyclodecane, cyclodecene or amixture thereof, etc., preferably cyclopropene, cyclobutene,cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclononene,cyclodecene or a mixture thereof, and most preferably cyclohexene.

The aliphatic or alicyclic hydrocarbon solvent may be used as a basesolvent when mixing the compounds in the preparation of theoligomerization catalyst system, may be used as a diluting solvent whenmixing the transition metal compound and the ligand compound, may be asolvent for diluting the cocatalyst, and at the same time may be asolvent used when mixing the transition metal compound, the ligandcompound and the cocatalyst. In addition, the aliphatic or alicyclichydrocarbon solvent may include other organic solvents in addition tothese solvents, but preferably may include only the aliphatic oralicyclic hydrocarbon compounds.

In the catalyst system for olefin oligomerization including the ligandcompound, the chromium compound, the metal alkyl compound, and thealiphatic or alicyclic hydrocarbon solvent, the three components of theligand compound, the chromium compound, and the metal alkyl compound maybe added together, simultaneously or sequentially in any order thereof,in the aliphatic or alicyclic hydrocarbon solvent, in the presence orabsence of monomers to obtain an active catalyst.

Another aspect of the present invention provides a method for preparingan olefin oligomer.

A method for preparing an olefin oligomer according to the presentinvention includes oligomerizing olefins in an inert solvent that doesnot react with a catalyst system in the presence of the catalyst systemfor olefin oligomerization including: a ligand compound represented byChemical Formula 1 or 2 above; a chromium compound; a metal alkylcompound; and an aliphatic or alicyclic hydrocarbon solvent.

The method for preparing an olefin oligomer according to the presentinvention improves the activity of the reaction by using the catalystsystem for olefin oligomerization. In this case, the olefin ispreferably an ethylene.

In the present invention, the olefin oligomerization may be performed asa homogeneous liquid phase reaction, a slurry reaction in which thecatalyst system is partially or completely insoluble, a two-phaseliquid/liquid reaction, a bulk phase reaction in which product olefinsserve as main media, or a gas phase reaction in the presence or absenceof an inert solvent by using the catalyst system for olefinoligomerization and a conventional apparatus and contacting techniques,and preferably a homogeneous liquid phase reaction may be employed.

The inert solvent in the present invention may be an aliphatic oralicyclic hydrocarbon solvent having 3 to 13 carbon atoms. Non-limitingexamples of the aliphatic or cycloaliphatic hydrocarbon solvents mayinclude n-heptane, 2-methylhexane, 3-methylhexane, 3-ethylpentane,2,3-dimethylpentane, 2,4-dimethylpentane, 2,2-dimethylpentane,3,3-dimethylpentane, 2,2,3-trimethylbutane, cyclopropane, cyclopropene,cyclobutane, cyclobutene, cyclopentane, cyclopentene, cyclohexane,cyclohexene, cycloheptane, cycloheptene, cyclooctane, cyclooctene,cyclononane, cyclononene, cyclodecane, cyclodecene or mixtures thereof,preferably a cycloalkene having 3 to 13 carbon atoms containing at leastone carbon-carbon double bond in a ring, more preferably a cycloalkenehaving 3 to 13 carbon atoms satisfying C_(n)H_(2n−2), even morepreferably a cycloalkene having 5 to 13 carbon atoms satisfyingC_(n)H_(2n−2), and most preferably cyclohexene, cyclooctene orcyclodecene. In this case, the solvent may be used by removing a smallamount of water or air that acts as a catalytic poison by treating witha small amount of alkylaluminum.

The olefin oligomerization reaction may be carried out at a temperatureof 0 to 250° C., preferably 20 to 200° C., and more preferably 40 to130° C. It is preferred to allow the reaction to proceed in the abovetemperature range because too low a reaction temperature may cause anexcessively large amount of unwanted insoluble products such as polymersto be produced, and too high a temperature may cause decomposition ofthe catalyst system and reaction products. In addition, the olefinoligomerization reaction may be carried out at a pressure of 1 to 200bar, and preferably at a pressure of 10 to 150 bar. Too low a reactionpressure may result in low catalytic activity. In addition, in theprocess for preparing the olefin oligomer, hydrogen may be added to thereactor at 0.01 to 50 bar, and preferably 0.5 to 10 bar in order topromote the reaction or increase the activity of the catalyst system.

Hereinafter, the present invention will be described in more detail withreference to Examples.

Preparation Example 1 Ligand Compound Preparation

In an inert atmosphere (nitrogen), triethylaluminum (63.1 mmol) wasdissolved in toluene (60 mL) in a 1-neck flask, 2,6-dimethylmorpholine(15.8 mmol) was then added thereto, and the reactant was stirred at roomtemperature for 5 hours. Then, toluene and unreacted triethylaluminumwere removed by distillation under reduced pressure (0.3 mmHg, 70° C.)to prepare a ligand compound represented by Chemical Formula 3 below:

EXAMPLES Catalyst System Preparation Example 1

By using chromium(III) 2-ethylhexanoate (21.3 mmol),2,6-dimethylmorpholine (63.8 mmol), ethyl aluminum dichloride (85.1mmol) and triethylaluminum (319 mmol), a representative catalyst systemwas prepared in an inert atmosphere (nitrogen). Specifically,chromium(III) 2-ethylhexanoate was dissolved in 30 mL of anhydrouscyclohexene and ligands were added. In a separate container,ethylaluminum dichloride and triethylaluminum were mixed together. Thealuminum alkyl solution was then slowly poured into the chromium/ligandsolution.

The reaction solution was stirred for 5 minutes and then the solvent wasremoved in vacuum. The remaining oily liquid was diluted to 150 mL withcyclohexene and the solution was filtered to remove black precipitatefrom the filtrate containing the catalyst system and diluted to a volumeof 250 mL with cyclohexene to prepare the final catalyst system.

Example 2

A catalyst system was prepared in the same manner as in Example 1,except that chromium(III) acetylacetonate was used instead ofchromium(III) 2-ethylhexanoate in Example 1.

Example 3

A catalyst system was prepared in the same manner as in Example 1,except that bis(2-ethylhexanoate) chromium(III) hydroxide was usedinstead of chromium(III) 2-ethylhexanoate in Example 1.

Example 4

A catalyst system was prepared in the same manner as in Example 1,except that the ligand compound prepared according to PreparationExample 1 was used instead of 2,6-dimethylmorpholine in Example 1.

Example 5

A catalyst system was prepared in the same manner as in Example 1,except that chromium(III) acetylacetonate was used instead ofchromium(III) 2-ethylhexanoate and the ligand compound preparedaccording to Preparation Example 1 was used instead of2,6-dimethylmorpholine in Example 1.

Example 6

A catalyst system was prepared in the same manner as in Example 1,except that bis(2-ethylhexanoate) chromium(III) hydroxide was usedinstead of chromium(III) 2-ethylhexanoate and the ligand compoundprepared according to Preparation Example 1 was used instead of2,6-dimethylmorpholine in Example 1.

Comparative Example

By using chromium(III) 2-ethylhexanoate (21.3 mmol), 2,5-dimethylpyrrole(63.8 mmol), ethyl aluminum dichloride (85.1 mmol) and triethylaluminum(319 mmol), a representative catalyst system was prepared in an inertatmosphere (nitrogen). Specifically, chromium(III) 2-ethylhexanoate wasdissolved in 30 mL of anhydrous toluene and ligands were added. In aseparate container, ethylaluminum dichloride and triethylaluminum weremixed together. The aluminum alkyl solution was then slowly poured intothe chromium/ligand solution. The reaction solution was stirred for 5minutes, and then the solvent was removed in vacuum. The remaining oilyliquid was diluted to 150 mL with cyclohexene and the solution wasfiltered to remove black precipitate from the filtrate containing thecatalyst system and diluted to a volume of 250 mL with toluene toprepare the final catalyst system.

Experimental Example

After filling the 2 L stainless steel reactor with nitrogen, 1 L of eachanhydrous polymerization solvent shown in Table 1 was added thereto, and3 mL of triethylaluminum was added thereto, followed by filling with 10bar of ethylene and raising the temperature to 90° C. After eachprepared catalyst solution (30 μmol) was injected to a reactor, ethylenewas charged to 35 bar, and the reactant was stirred at a stirring speedof 500 rpm. After one hour, the ethylene feed to the reactor wasstopped, the stirring was stopped to stop the reaction and the reactorwas cooled down below 10° C. After releasing excess ethylene in thereactor, ethanol mixed with 10 vol % hydrochloric acid was injected intothe liquid contained in the reactor. A small amount of organic layersample was passed through silica gel and dried, and then analyzed byGC-FID. The remaining organic layer was filtered to separate the solidwax/polymer product. These solid products were dried in an 80° C. ovenfor 8 hours and weighed to obtain polyethylene, and the results areshown in Table 1 below.

TABLE 1 Activity (Kg of Anhydrous 1- 1- Product/ polymerization hexeneoctene mmol of PE Division solution (wt %) (wt %) cat.) (wt %) Example 1Cyclohexene 45.3 51.2 3.8 3.5 Cyclooctene 46.3 50.6 3.2 3.1 Example 2Cyclohexene 46.9 50.0 4.3 3.1 Cyclooctene 44.2 52.3 4.1 3.5 Example 3Cyclohexene 41.2 55.2 4.7 3.6 Cyclooctene 42.1 54.7 4.1 3.2 Example 4Cyclohexene 48.9 47.8 3.2 3.3 Cyclooctene 49.2 47.3 2.7 3.5 Example 5Cyclohexene 50.1 46.7 3.6 3.2 Cyclooctene 49.9 46.8 3.4 3.3 Example 6Cyclohexene 49.8 46.5 5.0 3.7 Cyclooctene 50.0 46.3 4.3 3.7 ComparativeCyclohexane 99.3 0 3.1 0.7 Example

As shown in Table 1, as a result of the ethylene oligomerizationreaction using the catalyst system according to the present invention,it can be confirmed that 1-hexene and 1-octene can be preparedsimultaneously with high selectivity of 90 wt % or more, preferably 95wt % or more (Examples 1 to 6), and it can be seen to exhibit excellentactivity compared to the conventional (Comparative Example).

Hitherto, the preferred examples of the present invention have beendescribed in detail. The description of the present invention is onlyfor illustration, and it could be understood that particular embodimentcould be easily changed without changing the technical spirit oressential features of the present invention by one of ordinary skilledin the art.

Accordingly, it should be interpreted that the scope of the presentinvention is represented by claims hereinafter rather than the detaileddescription, and all changes or modifications derived from the meaning,range and equivalent concept of claims are included in the scope of thepresent invention.

The invention claimed is:
 1. A catalyst system for olefinoligomerization comprising: a ligand compound represented by ChemicalFormula 2 below; a chromium compound; a metal alkyl compound; and analiphatic or alicyclic hydrocarbon solvent,

wherein, in Chemical Formula 2, E₁ is boron (B), nitrogen (N), silicon(Si), or phosphorus (P), and E₂ is carbon (C), B₁ is aluminum (Al),boron (B), nitrogen (N), or phosphorus (P), R₁ to R₆ are eachindependently hydrogen, an alkyl group having 1 to 20 carbon atoms, acycloalkyl group having 3 to 20 carbon atoms, an alkylsilyl group having1 to 20 carbon atoms, a haloalkyl group having 1 to 20 carbon atoms, anaryl group having 6 to 40 carbon atoms, an arylalkyl group having 7 to20 carbon atoms, an arylsilyl group having 6 to 20 carbon atoms, analkylaryl group having 7 to 20 carbon atoms, an aryloxy group having 6to 20 carbon atoms, a halogen group, or an amino group.
 2. The catalystsystem of claim 1, wherein the chromium compound is a compoundcontaining chromium(III) or chromium(II).
 3. The catalyst system ofclaim 1, wherein the metal alkyl compound is at least one selected fromthe group consisting of an alkylaluminum compound, an alkylboroncompound, an alkylmagnesium compound, an alkylzinc compound, and analkyllithium compound.
 4. The catalyst system of claim 1, wherein themolar ratio of the ligand compound, the chromium compound, and the metalalkyl compound is 0.5:1:1 to 10:1:10,000 with respect to the chromiumcompound.
 5. The catalyst system of claim 1, wherein the aliphatic oralicyclic hydrocarbon solvent is an aliphatic or alicyclic hydrocarbonsolvent having 5 to 13 carbon atoms.
 6. The catalyst system of claim 5,wherein the alicyclic hydrocarbon solvent is a cycloalkene having 5 to13 carbon atoms.
 7. The catalyst system of claim 5, wherein thealiphatic or alicyclic hydrocarbon solvent is n-heptane, 2-methylhexane, 3-methyl hexane, 3-ethyl pentane, 2,3-dimethyl pentane,2,4-dimethyl pentane, 2,2-dimethyl pentane, 3,3-dimethyl pentane,2,2,3-trimethyl butane, cyclopropene, cyclobutene, cyclopentene,cyclopentane, cyclohexene, cycloheptane, cycloheptene, cyclooctane,cyclooctene, cyclononene, cyclodecane, cyclodecene, or a mixturethereof.
 8. A method for preparing an olefin oligomer, the methodcomprising oligomerizing olefins in an inert solvent that does not reactwith a catalyst system in the presence of the catalyst system for olefinoligomerization comprising: a ligand compound represented by ChemicalFormula 2 below; a chromium compound; a metal alkyl compound; and analiphatic or alicyclic hydrocarbon solvent,

wherein, in Chemical Formula 2, E₁ is boron (B), nitrogen (N), silicon(Si), or phosphorus (P), and E₂ is carbon (C), B₁ is aluminum (Al),boron (B), nitrogen (N), or phosphorus (P), R₁ to R₆ are eachindependently hydrogen, an alkyl group having 1 to 20 carbon atoms, acycloalkyl group having 3 to 20 carbon atoms, an alkylsilyl group having1 to 20 carbon atoms, a haloalkyl group having 1 to 20 carbon atoms, anaryl group having 6 to 40 carbon atoms, an arylalkyl group having 7 to20 carbon atoms, an arylsilyl group having 6 to 20 carbon atoms, analkylaryl group having 7 to 20 carbon atoms, an aryloxy group having 6to 20 carbon atoms, a halogen group, or an amino group.
 9. The method ofclaim 8, wherein the olefin oligomerization comprises a trimerizationand a tetramerization.
 10. The method of claim 8, wherein the inertsolvent is an aliphatic or alicyclic hydrocarbon solvent having 3 to 13carbon atoms.
 11. The method of claim 10, wherein the aliphatic oralicyclic hydrocarbon solvent is n-heptane, isobutane, 2-methyl hexane,3-methyl hexane, 3-ethyl pentane, 2,3-dimethyl pentane, 2,4-dimethylpentane, 2,2-dimethyl pentane, 3,3-dimethyl pentane, 2,2,3-trimethylbutane, cyclopropane, cyclopropene, cyclobutane, cyclobutene,cyclopentane, cyclopentene, cyclohexane, cyclohexene, cycloheptane,cycloheptene, cyclooctane, cyclooctene, cyclononane, cyclononene,cyclodecane, cyclodecene, or a mixture thereof.